SimScale CAE Forum

Multi region mesh problem concerning MRF and cell zone


Hello, I’m trying to simulate forces on a propeller and I used MRF for rotation. The meshing is done but when the simulation begin there is a multi region mesh problem. I don’t understand how to fix this issue.

Here is my project



Hey @WarChitect,

MRFs are currently not supported for tet-dominant meshes (standard meshing tool). They require a special treatment, where you have to assign a cellzone to the volumes that will be spinning.
Please refer to this tutorial on propellers with MRF. It’s quite similar to your project. Should you have any difficulties, do post an update here.



Thanks for your reply. I don’t think I understood the tutorial in full but I think that I only need to change the mesh type to an hex-dominant parametric?


Yes, that is a start :wink: (or Hex Parametric for more control)


From that tutorial. the most important step is to define a cell zone for the MRF.


YEP, I missed that one in the beginning, it is a very important parameter to select during the meshing process (MRFs need their own ‘With cell zone’ mesh refinement)…


Thanks for your help, I think I did what the turorial said but there is still an error that I don’t understand. Any advice ?


When using the parametric hex-dominant meshing tool without running a volume extraction operation beforehand, you have to click on this button after the mesh is finished:

Your mesh had some issues. The aspect ratio of your cells could be better. You want values close to 1 (cubic cells):

Extending the domain a little bit is also a good idea, to give some room for the flow to settle.

To save you some trouble, I drafted one mesh to get you started, which you can find in this link
There’s definitely things I encourage you to play with, like domain size, bounding box resolution, refinements etc.
In this project you will also find a converged run using the draft mesh. I chose to use a combination of velocity inlet and a custom outlet BC but there should be other combinations possible (and more representative than this one even).



Okay thank you a lot, I used a lot of what you did and it workded !


Hello, I am a bit sorry but I have another issue as soon as I change the mesh parameters the mesh is computed correctly but then there is an error with no explanation why in the simulaion.


You didn’t have a mesh selected for the errored sim runs…


Oups, sorry